1. Field of the Invention
The present invention relates to physiological data acquisition systems, such as polysomnography systems, and in particular to a method and apparatus for selecting differential input leads for such a system.
2. Description of the Related Art
Polysomnography, also known as a sleep study, is a multi-parametric test that is used for the purpose of diagnosing sleep disorders in people. During polysomnography, physiological data is acquired from a patient while he or she sleeps for subsequent analysis by a trained clinician. In a typical polysomnograph, the monitored parameters include such things as electrical encephalographic activity (via an electroencephalogram (EEG)); eye movements (via an electrooculogram (EOG)), muscle activity (via an electromyogram (EMG), heart rhythm (via an electrocardiogram (ECG)), respiratory effort, nasal and/or oral airflow, blood oxygen saturation (SpO2), body position, exhalation CO2, esophageal pH, and breathing sounds (for snoring). These parameters are typically each monitored during sleep by sensors that produce analog signals which are then transmitted to an acquisition device where the data is processed and stored for analysis by a trained clinician.
For a number of the parameters that are monitored during a polysomnograph, the sensors that collect the data are electrical leads that are attached to the patient's body. For example, a polysomnograph often includes collection of EMG data relating to leg movements by attaching leads to the legs of the patient and facial muscle movement and tension by attaching leads to the patient's chin. EEG, EOG, and ECG are also monitored using electrical leads attached to the patient's body.
A recurring problem in polysomnography is the detachment of such leads from the patient during the study as a result of, for example, patient movement during sleep. When a lead becomes detached, a signal is lost from a key sleep parameter or diagnostic indicator, which adversely affects the quality of testing. In addition, detached lead(s), if discovered, require intervention by someone during the study to reattach the lead(s) to the patient. Should the clinician choose to try to reattach the lead(s), they will need to enter the patient's room, turn on the lights, and awaken the patient. This causes a disruption in the patient's sleep and a disruption in the study, since a minimum number of hours of sleep must be recorded. And, again, the clinician will need to repeat the process of traveling back and forth between the patient room and the central control room to assure the impedance is at an acceptable level upon reapplication of the leads.